The design and use of filter circuitry for filtering a signal of undesired frequency is well known. It is also known that these filters can be fabricated from ceramic materials having one or more resonators formed therein.
Many conventional ceramic block filters are comprised of parallelepiped shaped blocks of dielectric material through which many holes extend from one surface to the opposite surface. Often, these filters use printed capacitors on the top surface to obtain the desired frequency characteristics of the filter. Another method used to control the frequency characteristic of the filter involves removing ceramic material from one or more surfaces of the block to form embedded features in the ceramic block filter.
Removing material from the surface of the block can lead to a variety of problems during the processing of the ceramic block filter. For example, during the forming stage, embedded features must be capable of being pressed. During firing, the embedded features must not cause the filter to slump or crack. During a post-firing metallization operation, the embedded features must be capable of being easily coated with a viscous material.
It would be considered an improvement in the art to provide a channeled filter which has embedded features on one surface of the ceramic block and that provided an improved frequency response in the form of a high side, low side, or split transmission zero.